Preparation of 3-pentenoic acid esters by carbonylation of alkoxybutenes

ABSTRACT

3-Pentenoic esters are prepared by carbonylation of alkoxybutenes in the presence of a catalyst and a solvent at elevated temperature and elevated pressure, by reacting at least one C 1  -C 10  -alkoxybutene in which the alkoxy group is in the allyl position relative to the double bond with carbon monoxide at from 60 to 140° C. and a carbon monoxide partial pressure in the range from 3 to 30 MPa in the presence of a catalyst based on palladium.

The present invention relates to a process for preparing 3-pentenoicesters by carbonylation of alkoxybutenes in the presence of a catalystand a solvent at elevated temperature and elevated pressure.

EP-A 301 450 and EP-A 351 616 disclose processes for preparing alkylpentenoates by reacting butadiene with carbon monoxide and alcohols inthe presence of cobalt carbonyl complexes and tertiary nitrogen bases.These processes require high pressures of from 120 to 700 bar and formmixtures of 2-, 3- and 4-pentenoic esters.

GB-A 1 110 405 describes a process for preparing pentenoic esters bycarbonylation of butadiene in the presence of an alcohol using platinum,palladium and/or nickel catalysts. Here too, high pressures of from 100to 1000 bar are required.

EP-A 60 734 discloses a process for preparing pentenoic esters bycarbonylation of butadiene in the presence of an alcohol, a hydrogenhalide and a palladium catalyst at lower pressures around 150 bar. Adisadvantage of this process is that a large excess of corrosivehydrogen halide is required (molar ratio of hydrogen halide to palladiumis 20-100:1).

According to EP-A 284 170 and EP-A 271 145, pentenoic esters can beprepared by carbonylation of butadiene in the presence of alcohols usingpalladium compounds, phosphines and acids. This does not give the3-pentenoic ester in pure form, but in admixture with its isomers.

Another way of preparing β,γ-unsaturated esters is described in U.S.Pat. No. 4,622,416. Carbonylation of allyl ethers catalyzed by nickel,cobalt or iron halides gives the esters. A disadvantage of this processis the formation of product mixtures. The carbonylation of8-methoxy-1,6-octadiene gives not only methyl 3,8-nonadienoate but alsothree cyclic carboxylic acid compounds. Satisfactory selectivities(maximum 91%) can only be obtained at a pressure above 170 bar and atemperature of 150° C. Under these conditions the catalyst lossresulting from formation of volatile nickel compounds is very high.

EP-A 217 407 describes the carbonylation of allyl ethers with PdCl₂/CuCl₂ catalysis to give unsaturated esters. Here, large amounts oftetrabutylammonium chloride (25 mol % based on starting material) areadded to the reaction mixture for extraction of the product. Thisaddition leads to extensive precipitation of metallic palladium.

EP-A 514 288, EP-A 478 471 and EP-A 433 191 disclose the doublecarbonylation of 1,4-butenediols and 1,4-dialkoxybutenes to givedehydroadipic acid (diesters) using palladium compounds and chloridessuch as alkali metal, alkaline earth metal or quaternary ammonium orphosphonium halides. These processes require a large excess of chloride(typical molar ratios of Pd to chloride of from 1:17 to 1:27) or elselarge amounts of PdCl₂ of about 20 mol %, based on the startingmaterial.

It is an object of the present invention to provide a process forpreparing 3-pentenoic esters containing a very low proportion ofisomeric 2- and 4-pentenoic esters by carbonylation of alkoxybutenes inthe presence of a catalyst based on palladium under mild conditions.

We have found that this object is achieved by a process for preparing3-pentenoic esters by carbonylation of alkoxybutenes in the presence ofa catalyst and a solvent at elevated temperature and elevated pressure,by reacting at least one C₁ -C₁₀ -alkoxybutene in which the alkoxy groupis in the allyl position relative to the double bond with carbonmonoxide at from 60 to 140° C. and a carbon monoxide partial pressure inthe range from 3 to 30 MPa in the presence of a catalyst based onpalladium.

In addition, we have found a homogeneous catalyst system in which nocatalyst deactivation occurs as a result of palladium precipitation ifthe carbonylation is carried out in the additional presence ofquaternary ammonium or phosphonium salts or specific phosphines.

The starting materials used in the process of the invention include atleast one C₁ -C₁₀ -alkoxybutene, preferably a C₁ -C₄ -alkoxybutene, inwhich the alkoxy group is in the allyl position relative to the doublebond. Preference is given to 3-methoxy-1-butene, 3-ethoxy-1-butene,3-n-propoxy-1-butene, 3-n-butoxy-1-butene, trans-1-methoxy-2-butene,trans-1-ethoxy-2-butene, trans-1-n-propoxy-2-butene,trans-1-n-butoxy-2-butene, cis-1-methoxy-2-butene,cis-1-ethoxy-2-butene, cis-1-n-propoxy-2-butene,cis-1-n-butoxy-2-butene, and mixtures thereof, particularly a mixture of3-methoxy-1-butene, trans-1-methoxy-2-butene and cis-1-methoxy-2-butene.

The starting compounds can be prepared according to U.S. Pat. No.2,922,822 by acid-catalyzed alcohol addition to butadiene.

The catalyst used according to the invention is a catalyst based onpalladium. Preference is given to using palladium compounds in theoxidation states 0, +1 or +2, which can be present as palladium salts orpalladium complexes, in particular PdCl₂, PdCl₂ -(benzonitrile)₂, PdCl₂(acetonitrile)₂, Pd(OAc)₂, bis(allylchloropalladium) complexes anddichlorodiphosphinepalladium complexes. Such compounds are known tothose skilled in the art, for example from Dictionary of organometallicCompounds, Vol. 2, 1984, Chapman and Hall, pp. 1484-1544.

The molar ratio of palladium compound to alkoxybutene (or the sum of themoles of the alkoxybutenes used) is usually in the range from 0.1:1 to10:1, preferably from 0.5:1 to 5:1.

In a preferred embodiment, the activity and/or the stability of thepalladium catalyst can be increased by addition of chlorides, acids,nitrogen-containing or phosphorus-containing ligands (hereinafterreferred to altogether as additives). Chlorides used are preferablyalkali metal, alkaline earth metal, transition metal, quaternaryammonium and phosphonium chlorides such as lithium, sodium, potassiumchloride, preferably sodium chloride, magnesium, calcium, strontium,barium dichloride, preferably calcium dichloride, copper dichloride,silver chloride, gold trichloride, preferably copper dichloride, andalso compounds of the general formula R¹ R² R³ R⁴ NCl, R¹ R² R³ R⁴ PClor (R⁵)₃ N═P═N(R⁵)₃, where R¹ to R⁴ are identical or different and arealiphatic groups having from 1 to 10 carbon atoms, preferably from 4 to8 carbon atoms, and/or unsubstituted or substituted aryl groups, R⁵ isan aryl group having 6-10 carbon atoms which is unsubstituted orsubstituted by alkyl groups, alkoxy groups or alkoxycarbonyl groupshaving 1-4 carbon atoms or by halogen, particular preference being givento using tetrabutylammonium chloride, tetrabutylphosphonium chloride andbis(triphenylphosphine)imimium chloride.

Acids preferably used are inorganic and organic protic acids such ashydrochloric acid, sulfuric acid, phosphoric acid, tetrafluoroboric acidor sulfonic acids such as methanesulfonic acid and p-toluenesulfonicacid or Lewis acids such as boron trifluoride-diethyl ether complex andaluminum trichloride.

Phosphorus compounds preferably used are phosphines having the generalformula R⁶ R⁷ R⁸ P, where R⁶ to R⁸ are identical or different and arealiphatic groups having from 1 to 10 carbon atoms, preferably from 4 to8 carbon atoms, unsubstituted or substituted aryl or unsubstituted orsubstituted heteroaryl groups having from 6 to 10 carbon atoms,preferably phenyl, pyridyl and pyrimidyl groups. Examples which may bementioned are triphenylphosphine, tricyclohexylphosphine,tris(2-methoxyphenyl)phoshine, tris(3-methoxyphenyl)phosphine,tris(4-methoxyphenyl)phosphine and 2-diphenylphosphinopyridine.

Other phosphorus compounds which can be used are multidentate chelateligands such as bis(diphenylphosphino)methane,1,2-bis-(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane,1,4-bis(diphenylphosphino)butane and bis(di-tert-butylphosphino)methane.

In general, the molar ratio of additive to palladium is chosen withinthe range from 0.1 to 10, preferably from 0.5 to 4.

According to the invention, the carbonylation is carried out at from 60to 140° C., preferably from 80 to 120° C., and at a carbon monoxidepartial pressure in the range from 3 to 30 MPa, preferably from 5 to 15MPa.

Furthermore, the carbonylation can be carried out batchwise orcontinuously.

In addition, the carbonylation can be carried out in the presence of asolvent, with the weight ratio of solvent to alkoxybutene(s) generallybeing chosen in the range from 0.5:1 to 15:1, preferably from 2:1 to10:1.

Solvents used are

aliphatic, cycloaliphatic or aromatic alcohols having from one to tencarbon atoms, preferably from one to four carbon atoms, preference beinggiven to using alcohols ROH whose RO radical corresponds to the C₁ -C₁₀-alkoxy radical of the alkoxybutene used, preferably methanol, ethanol,n-propanol and n-butanol;

aliphatic or aromatic nitriles having from two to ten carbon atoms,preferably benzonitrile, acetonitrile, propionitrile;

ureas having from five to fifteen carbon atoms, preferablytetramethylurea, dimethylethyleneurea, dimethylpropyleneurea;

acid amides having from three to ten carbon atoms, preferablydimethylformamide, dibutylformamide, dimethylacetamide,N-methyl-2-pyrrolidone;

carbamic esters having from four to thirteen carbon atoms such as3-methyl-2-oxazolidinone;

hydrocarbons having from five to ten carbon atoms such as benzene andtoluene;

ethers having from two to sixteen carbon atoms such as methyl tert-butylether, diphenyl ether;

and mixtures thereof.

The 3-pentenoic esters which can be prepared according to the inventionare important intermediates for preparing, for example, adipic acid,caprolactam and caprolactone and also their polymers and copolymers suchas polyamide-6 and polyamide-66.

The advantages of the process of the invention compared with processesof the prior art are that high pressures, ie. pressures of more than 30MPa, can be avoided, that high yields are achieved, that 3-pentenoicesters are obtained in high isomeric purity, that isomer mixtures ofalkoxybutenes can be used, that the process can also be carried outcontinuously and that the catalyst can be recycled without great loss inactivity.

EXAMPLES

In all examples, the yields were determined by gas chromatography. No4-pentenoic ester could be detected. In the Examples 1 to 19, less than2% of 2-pentenoic ester, based on the respective 3-pentenoic ester, wasformed.

Example 1

A mixture of 61.48 mmol of 3-methoxy-1-butene, 48.72 mmol oftrans-1-methoxy-2-butene, 5.8 mmol of cis-1-methoxy-2-butene, 5.6 mmolof PdCl₂ and 45 g of methanol were treated at room temperature with 10MPa of carbon monoxide in a 300 ml autoclave. The mixture wassubsequently heated to 80° C. and stirred for 5 hours at thistemperature and the pressure which was established (12 MPa). It was thencooled to room temperature and the pressure was brought to atmosphericpressure. The yield of methyl 3-pentenoate was 60%.

Examples 2 to 4

A mixture of 53.0 mmol of 3-methoxy-1-butene, 42.0 mmol oftrans-1-methoxy-2-butene, 5.0 mmol of cis-1-methoxy-2-butene, 2.5 mmolof PdCl₂ and 40 g of a solvent (see Table 1) was treated at roomtemperature with 5 MPa of carbon monoxide in a 300 ml autoclave. Themixture was subsequently heated (for temperature see Table 1) andstirred for 5 hours at this temperature and a pressure of 10 MPa. It wasthen cooled to room temperature and the pressure was brought toatmospheric pressure. The yield of methyl 3-pentenoate is likewise shownin Table 1.

                  TABLE 1                                                         ______________________________________                                        Example                                                                              Solvent        Temperature [° C.]                                                                  Yield [%]                                  ______________________________________                                        2      dimethylpropyleneurea                                                                         80          57                                           3 benzonitrile 100 61                                                         4 MeOH/benzonitrile (1:1) 100 61                                            ______________________________________                                    

Examples 5 to 18

A mixture of 53.0 mmol of 3-methoxy-1-butene, 42.0 mmol oftrans-1-methoxy-2-butene, 5.0 mmol of cis-1-methoxy-2-butene, 2.5 mmolof PdCl₂, from 2.5 to 10 mmol of an additive (see Table 2) and 40 g of asolvent (see Table 2) was treated at room temperature with 10 MPa ofcarbon monoxide in a 300 ml autoclave. The mixture was subsequentlyheated to 100° C. and stirred for 5 hours at this temperature and at thepressure which was established (<13 MPa). It was then cooled to roomtemperature and the pressure was brought to atmospheric pressure. Theyield of methyl 3-pentenoate is likewise shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                              Additive       Yield                                      Ex. Solvent (mol per mol of Pd) [%]                                         ______________________________________                                         5   benzonitrile     CuCl.sub.2  (1)                                                                              75                                          6 " AlCl.sub.3  (1) 72                                                        7 " Bu.sub.4 PCl (2) 39                                                       8 " Bu.sub.4 NCl (1) 60                                                       9 " Ph.sub.2 PPy, MSA (1/1) 74                                               10 " Ph.sub.2 PPy, MSA (4/4) 56                                               11 NMP Bu.sub.4 NCl (1) 71                                                    12 " P(o-CH.sub.3 OC.sub.6 H.sub.4).sub.3  (1) 77                             13 " Ph.sub.2 PPy, p-TosOH (4/4) 63                                           14 3-methyl-2-oxazolidinone Ph.sub.2 PPy, MSA (4/4) 58                        15 " Bu.sub.4 NCl (1) 73                                                      16 tetramethylurea Ph.sub.2 PPy, MSA (4/4) 58                                 17 dimethylpropyleneurea Ph.sub.2 PPy, MSA (4/4) 57                           18 dimethylacetamide Bu.sub.4 NCl (1) 64                                    ______________________________________                                         NMP = Nmethylpyrrolidone                                                      Ph.sub.2 PPy = 2diphenylphosphinopyridine                                     MSA = methylsulfonic acid                                                

Example 19

A mixture of 26.5 mmol of 3-methoxy-1-butene, 21 mmol oftrans-1-methoxy-2-butene, 2.5 mmol of cis-1-methoxy-2-butene, 2.5 mmolof Pd(OAc)₂, 5 mmol of 1,4-bis(diphenylphosphino)butane and 50 g oftoluene was treated at room temperature with 10 MPa of carbon monoxidein a 300 ml autoclave. The mixture was subsequently heated to 110° C.and stirred for 20 hours at this temperature and at the pressure whichwas established (11 MPa). It was then cooled to room temperature and thepressure was brought to atmospheric pressure. The yield of methyl3-pentenoate. was 35%.

Example 20

5.25 g/h of a solution of the composition 48.0% by weight ofmethoxybutene isomer mixture (molar ratio 3-methoxy-1-butene:trans-1-methoxy-2-butene: cis-1-methoxy-2-butene=49:45:6) inN-methyl-2-pyrrolidone (NMP) and 11.9 g/h of catalyst solution of thecomposition 2.20% by weight of PdCl₂ and 7.36% by weight of Bu₄ NClhydrate in NMP plus 6 l/h of gaseous CO were continuously fed into anautoclave (volume: 94 ml) fitted with magnetic stirrer and thermostatedto 100° C. in an oil bath. The pressure was kept constant at 100 bar.21.0 g/h of liquid product was taken off continuously via a regulatorvalve. The yield of methyl 3-pentenoate was 73.6% at a conversion of85.5%. Methyl 2-pentenoate was formed in a yield of 5.1%. No Pdprecipitation was visible in the autoclave. 99% by weight of thepalladium used could be detected in dissolved form in the liquidreaction product.

Example 21

The experiment of Example 19 was repeated, except that 9.10 g/h of asolution of the composition 48.8% by weight of methoxybutene isomermixture (molar ratio 3-methoxy-1-butene: trans-1-methoxy-2-butene:cis-1-methoxy-2-butene=45:50:5) in NMP and 20.6 g/h of catalyst solutionof the composition 2.20% by weight of PdCl₂ and 7.36% by weight of Bu₄NCl hydrate in NMP were used. The yield of methyl 3-pentenoate was 69.4%at a conversion of 78.9%. Methyl 2-pentenoate was formed in a yield of3.4%. No Pd precipitation was visible in the autoclave. The palladiumused could be found quantitatively in dissolved form in the liquidreaction product.

The product and unreacted starting material were separated by Sambaydistillation (100° C., 30 mbar) and the catalyst-containing distillationresidue was reused in place of a fresh catalyst solution. Afterrecycling the catalyst solution three times in the manner justdescribed, a yield of methyl 3-pentenoate of 69.0% and a yield of methyl2-pentenoate of 3.4% were achieved at a conversion of 77.9%.

We claim:
 1. A process for preparing 3-pentenoic esters by carbonylationof alkoxybutenes in the presence of a catalyst and a solvent at elevatedtemperature and elevated pressure, which comprises reacting at least oneC₁ -C₁₀ -alkoxybutene in which the alkoxy group is in the allyl positionrelative to the double bond with carbon monoxide at a temperature in therange from 60 to 140° C. and a carbon monoxide partial pressure in therange from 3 to 30 MPa in the presence of a catalyst based onpalladium,wherein the carbonylation is carried out in the additionalpresence of an additive which increases the activity and/or stability ofthe palladium catalyst selected from the group consisting of chlorides,inorganic acids, and Lewis acids at a molar ratio of additive tocatalyst of from 0.1 to 10 wherein the molar ratio of catalyst toalkoxybutene is from 0.1:1 to 10:1 and wherein the process yieldsessentially no 4-pentenoic ester and less than 2% of 2-pentenoic esterbased on the respective 3-pentenoic ester.
 2. A process as claimed inclaim 1, wherein a mixture of trans-1-methoxy-2-butene andcis-1-methoxy-2-butene is used.
 3. A process as claimed in claim 1,wherein a mixture of 3-methoxy-1-butene, trans-1-methoxy-2-butene andcis-1-methoxy-2-butene is used.
 4. The process of claim 1 wherein themolar ratio of additive to catalyst is from 0.5 to
 4. 5. A process forpreparing 3-pentenoic esters by carbonylation of alkoxybutenes in thepresence of a catalyst and a solvent at elevated temperature andelevated pressure, which comprises reacting at least one C₁ -C₁₀-alkoxybutene in which the alkoxy group is in the allyl positionrelative to the double bond with carbon monoxide at a temperature in therange from 60 to 140° C. and a carbon monoxide partial pressure in therange from 3 to 30 MPa in the presence of a catalyst consistingessentially of a catalyst based on palladiumwherein essentially nofurther additive which increases the activity and/or stability of thepalladium catalyst is present and wherein the process yields essentiallyno 4-pentenoic ester and less than 2% of 2-pentenoic ester based on therespective 3-pentenoic ester.
 6. A process as claimed in claim 5,wherein a mixture of trans-1-methoxy-2-butene and cis-1-methoxy-2-buteneis used.
 7. A process as claimed in claim 5, wherein a mixture of3-methoxy-1-butene, trans-1-methoxy-2-butene and cis-1-methoxy-2-buteneis used.